<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>

  <script>
    function sum(n) {
      if (n == 1)
        return 1
      return n + sum(n - 1)
    }
    function mul(n) {
      if (n == 1)
        return 1
      return n * sum(n - 1)
    }

  </script>
</body>

</html>